Multi ratio drive

ABSTRACT

A multi ratio drive including a first drive chain having a first drive chain engaged state and a first drive chain disengaged state; and a second drive chain having a second drive chain engaged state and a second drive chain disengaged state. The first drive chain drives the axle with a first gear ratio between the drive shaft and the axle when the first drive chain is in the first drive chain engaged state and the second drive chain is in the second drive chain disengaged state; the second drive chain drives the axle with a second gear ratio between the drive shaft and the axle when the second drive chain is in the second drive chain engaged state and the first drive chain is in the first drive chain disengaged state; and the first gear ratio is different from the second gear ratio.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims the benefit of, U.S.patent application Ser. No. 14/710,139 filed May 12, 2015, which is acontinuation of, and claims the benefit of, U.S. patent application Ser.No. 14/320,031 filed Jun. 30, 2014, which is a continuation of, andclaims the benefit of, U.S. patent application Ser. No. 14/015,400 filedAug. 30, 2013, which is a continuation of, and claims the benefit of,U.S. patent application Ser. No. 12/687,724 filed Jan. 14, 2010, (nowU.S. Pat. No. 8,523,727), the entire disclosures of each which areincorporated herein by reference.

TECHNICAL FIELD

The field of this disclosure is drives for power transfer in vehicles,particularly, a multi ratio drive.

BACKGROUND

This invention is the idea of a mechanic with forty years in the field.The purpose of the invention is to increase the efficiency of the finaldrive unit in a vehicle by increasing performance and thereby using lessenergy. Vehicles, such as cars, pickup trucks, load hauling semitractors, and the like, typically have an engine that generates power, atransmission that provides speed-torque conversion for that power, and adrive that provides the converted power to the axle and wheels. Thecombination of the transmission, drive, and axle is known as the drivetrain.

In rear wheel drive vehicles, power passes from the engine to thetransmission, through the transmission to a drive shaft, and through thedrive shaft to a single ratio drive. The transmission changes therotation rate between the engine and the drive shaft. The single ratiodrive includes a pinion gear in contact with a ring gear, which changesthe plane of rotation from the drive shaft to the axles. A differentialattached to the ring gear allows the axles to turn independently of eachother and to turn the drive wheels.

In front wheel drive vehicles and rear engine, rear drive vehicles, theengine is mounted transversely (side to side) in the vehicle and theengine crankshaft turns in the same plane as the drive wheels. Atransaxle houses the transmission and the drive assembly in a singletransaxle case. Larger front wheel drive vehicles use a drive planetarygear set, which has a single ratio sun gear driven by the transmissionoutput shaft, and a drive assembly that has the planet assembly anddifferential assembly built together as one assembly. The single ratiosun gear drives several single ratio planet gears in contact with asingle ratio ring gear lugged to the transaxle case that the driveassembly walks around. Because the ring gear is lugged to the transaxlecase and does not turn, the differential assembly attached to the driveassembly turns, turning the axles and the wheels. smaller front wheeldrive vehicles use an idler gear driven by the transmission output shaftto drive a pinion gear, which drives a ring gear positively attached tothe differential assembly

Unfortunately, changes in the gear ratio between the engine and thewheels in the drive train of both rear wheel and front wheel drivevehicles are limited to the transmission: the drive is limited to asingle gear ratio. A high gear ratio, such as four-to-one, is desirablefor quick starts with high torque to get the vehicle moving, but isundesirable for high speed operation. A low gear ratio, such asone-to-one, is desirable for high speed operation, but is undesirable orunable to start vehicle motion. Typically, a compromise gear ratio ofthree-to-one is selected, but this is only efficient at mid rangespeeds. The compromise gear ratio wastes energy because the gear ratiois not matched to the operating speed. In addition, the gear ratiolimits the ability to attain maximum acceleration. Although the gearratio can be changed by disassembling the drive and changing out thegears, the gear ratio cannot be changed in operation.

It would be desirable to have a multi ratio drive that would overcomethe above disadvantages.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a multi ratio driveoperably connecting a drive shaft and an axle, the multi ratio driveincluding a first drive chain having a first drive chain engaged stateand a first drive chain disengaged state; and a second drive chainhaving a second drive chain engaged state and a second drive chaindisengaged state. The first drive chain drives the axle with a firstgear ratio between the drive shaft and the axle when the first drivechain is in the first drive chain engaged state and the second drivechain is in the second drive chain disengaged state; and the seconddrive chain drives the axle with a second gear ratio between the driveshaft and the axle when the second drive chain is in the second drivechain engaged state and the first drive chain is in the first drivechain disengaged state. The first gear ratio is different from thesecond gear ratio.

Another aspect of the present invention provides a multi ratio driveoperably connected to a drive shaft, the multi ratio drive including apinion gear rotatable by the drive shaft; a main shaft; a fixed ringgear fixed to the main shaft and engaged with the pinion gear; adifferential shaft; a first drive chain having a first main shaft ringgear lockable to the main shaft and a first differential shaft ring gearfixed to the differential shaft and engaged with the first main shaftring gear, the first drive chain having a first gear ratio; a seconddrive chain having a second main shaft ring gear lockable to the mainshaft and a second differential shaft ring gear fixed to thedifferential shaft and engaged with the second main shaft ring gear, thesecond drive chain having a second gear ratio; a differential operablyconnected to the differential shaft; a first axle operably connected tothe differential; and a second axle operably connected to thedifferential. The first drive chain operably connects the drive shaft tothe first axle and the second axle at a first gear ratio when the firstmain shaft ring gear is locked to the main shaft and the second mainshaft ring gear is not locked to the main shaft; and the second drivechain operably connects the drive shaft to the first axle and the secondaxle at a second gear ratio when the second main shaft ring gear islocked to the main shaft and the first main shaft ring gear is notlocked to the main shaft.

Yet another aspect of the present invention provides multi ratio driveincluding a housing; a piston longitudinally slideable in the housing; aring gear shell longitudinally slideable and rotatably fixed in thehousing, the ring gear shell being coupled to the piston and having afirst ring gear and a second ring gear; a sun gear shaft having a firstsun gear and a second sun gear; a planet gear assembly having a firstplanet gear operably connected to a planet carrier and a second planetgear operably connected to the planet carrier; a differential operablyconnected to the planet carrier; a first axle operably connected to thedifferential; and a second axle operably connected to the differential.A first drive chain comprises the first sun gear, the first planet gear,and the first ring gear, the first planet gear being engaged with thefirst sun gear and the first ring gear being engagable with the firstplanet gear; a second drive chain comprises the second sun gear, thesecond planet gear, and the second ring gear, the second planet gearbeing engaged with the second sun gear and the second ring gear beingengagable with the second planet gear; the first drive chain connectsthe sun gear shaft to the first axle and the second axle at a first gearratio when the piston positions the ring gear shell with the first ringgear being engaged with the first planet gear; and the second drivechain connects the sun gear shaft to the to the first axle and thesecond axle at a second gear ratio when the piston positions the ringgear shell with the second ring gear being engaged with the secondplanet gear.

The foregoing and other features and advantages of the invention willbecome further apparent from the following detailed description of thepresently preferred embodiments, read in conjunction with theaccompanying drawings. The detailed description and drawings are merelyillustrative of the invention, rather than limiting the scope of theinvention being defined by the appended claims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a multi ratio drive in accordance withthe present invention;

FIG. 2 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention;

FIG. 3A is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention;

FIG. 3B is a detailed side view of a synchronizer for use in a multiratio drive in accordance with the present invention;

FIGS. 4A and 4B are cutaway side views of multi ratio drives inaccordance with the present invention;

FIG. 5 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention;

FIG. 6 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention;

FIG. 7 is an end view of a ring gear shell for a multi ratio drive inaccordance with the present invention;

FIG. 8 is a side view of a sun gear shaft for a multi ratio drive inaccordance with the present invention;

FIG. 9 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention;

FIG. 10 is a side view of a sun gear shaft for a multi ratio drive inaccordance with the present invention;

FIG. 11 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention;

FIG. 12 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention;

FIG. 13 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of a multi ratio drive in accordance withthe present invention. The multi ratio drive operably connects a driveshaft and an axle to provide a number of gear ratios between the driveshaft and axle. The multi ratio drive includes a first drive chainhaving a first drive chain engaged state and a first drive chaindisengaged state, and at least a second drive chain having a seconddrive chain engaged state and a second drive chain disengaged state. Thefirst drive chain drives the axle with a first gear ratio between thedrive shaft and the axle when the first drive chain is in the firstdrive chain engaged state and the second drive chain is in the seconddrive chain disengaged state. The second drive chain drives the axlewith a second gear ratio between the drive shaft and the axle when thesecond drive chain is in the second drive chain engaged state and thefirst drive chain is in the first drive chain disengaged state. Thefirst gear ratio is different from the second gear ratio.

In the embodiment of FIG. 1, the first drive chain includes a first mainshaft ring gear engaged with a first differential shaft ring gear, thefirst main shaft ring gear being locked on a main shaft when the firstdrive chain is in the first drive chain engaged state and beingrotatable on the main shaft when the first drive chain is in the firstdrive chain disengaged state, and the first differential shaft ring gearbeing fixed on a differential shaft. The second drive chain includes asecond main shaft ring gear engaged with a second differential shaftring gear, the second main shaft ring gear being locked on the mainshaft when the second drive chain is in the second drive chain engagedstate and being rotatable on the main shaft when the second drive chainis in the second drive chain disengaged state, and the seconddifferential shaft ring gear being fixed on the differential shaft. Themulti ratio drive can be used for rear wheel drive vehicles or the like,with the drive shaft delivering power from the engine and the axle beinga straight axle or a pair of axles connected to the drive chains througha differential.

The multi ratio drive 30 includes a main shaft 40 rotatably supported ina housing 60 by bearings 62 and a differential shaft 50 rotatablysupported in the housing 60 by bearings 63. The housing 60 can containlubricant (not shown) for the components of the multi ratio drive 30within the housing 60, with seals (not shown) where any components passthrough the housing 60. A pinion gear 70 receives rotational power froma drive shaft 72 and transfers the power to a fixed ring gear 42 fixedto the main shaft 40, rotating the main shaft 40 about its longitudinalaxis. The main shaft 40 also has two or more main shaft ring gears 44,45, 46, 47, each of which has a locked state and a rotatable state. Inthe locked state, the main shaft ring gear is locked to and rotates withthe main shaft 40. In the rotatable state, the main shaft ring gear isfree from and rotates about the main shaft 40. Those skilled in the artwill appreciate that the main shaft ring gears 44, 45, 46, 47 can beswitched between the locked and rotatable states using slip clutches,which are responsive to rotational speed (rpm) of the main shaft 40 orcentrifugal force to engage and disengage the main shaft ring gears 44,45, 46, 47 with the main shaft 40. The slip clutch locks the main shaftring gear on the main shaft when the associated drive chain is in thedrive chain engaged state. Slip clutches as defined herein are clutcheswhich are operable to selectively engage or disengage gears to a shaftin response to a desired condition, such as desired rotational speed,desired centrifugal force, or the like. In one embodiment, the slipclutch can selectively engage or disengage the gears to the shaftregardless of the direction of shaft rotation.

The main shaft ring gears 44, 45, 46, 47 each mesh with one of thedifferential shaft ring gears 52, 53, 55, 56, which are fixed to androtate with the differential shaft 50. The differential shaft ring gears52, 53, 55, 56 and main shaft ring gears 44, 45, 46, 47 form drivechains 73, 74, 75, 76. The drive chains 73, 74, 75, 76 can havedifferent gear ratios (from tooth spacing, diameter, and the like) toallow the multi ratio drive 30 to operate at different gear ratiosbetween the drive shaft 72 and axles 56, 57. In one embodiment, thedifferential shaft 50 includes a differential 54 operably connected tothe axles 56, 57 to allow differential slip between the two axles 56,57. In another embodiment, the differential is omitted and the axle is asolid axle transferring power directly from the differential shaft ringgears 52, 53, 55, 56 to the load, such as vehicle wheels or a stationarymachine (e.g., a generator, water pump, hydraulic pump, or the like).

In operation, the drive shaft 72 rotates the pinion gear 70, causing themain shaft 40 to rotate through the pinion gear 70. When one of the mainshaft ring gears 44, 45, 46, 47 is in the locked state, the locked mainshaft ring gear rotates with the main shaft 40 and drives thedifferential shaft ring gear associated with the locked main shaft ringgear in the drive chain. The differential shaft ring gear rotates thedifferential shaft 50, which rotates the axles 56, 57 through thedifferential 54. The other main shaft ring gears in the rotatable state,i.e., not in the locked state, rotate about the main shaft 40, driven bythe differential shaft ring gear associated with the rotatable mainshaft ring gears in the drive chains, but transfer minimal power. Thegear ratio of the multi ratio drive 30 can be changed by unlocking thepresently locked main shaft ring gear and engaging one of the presentlyrotatable main shaft ring gears. Those skilled in the art willappreciate that a number of possible gear ratios can be provided,limited only by the space available in the housing 60 for the sets ofdrive chains 73, 74, 75, 76. Exemplary uses of the multi ratio drive arerear wheel drive cars, pickup trucks, load hauling semi tractors, andthe like.

FIG. 2, in which like elements share like reference numbers with FIG. 1,is a schematic diagram of another embodiment of a multi ratio drive inaccordance with the present invention. In this embodiment, the multiratio drive can drive an external load or stationary machine, such as agenerator, water pump, hydraulic pump, or the like. The axles 56, 57 ofthe multi ratio drive 80 can be coupled through gears, a chain, or thelike to drive one or more stationary machines 82. In one embodiment, thedifferential 54 is omitted and the axle 56 is a solid axle transferringpower directly from the differential shaft ring gears 52, 53 to theload.

The multi ratio drive 80 can also include a power take-off (PTO) 84coupled to one of the main shaft ring gears 44, 45. In this example, thepower take-off 84 includes a PTO coupling gear 86 engaged with the drivechain 74 through one of the main shaft ring gears 45, a PTO shaft 88,and a PTO driving gear 90 coupled to an external load 92. The main shaftring gear 45 has a locked and a rotatable state, so the power take-off84 can be engaged or disengaged from the load 92 by engaging ordisengaging the main shaft ring gear 45 from the main shaft 40.

FIG. 3A, in which like elements share like reference numbers with FIG.1, is a schematic diagram of another embodiment of a multi ratio drivein accordance with the present invention. In this embodiment, the mainshaft ring gears are engaged and disengaged from the main shaft using asynchronizer. The synchronizer can be disposed on the main shaft betweenthe first main shaft ring gear and the second main shaft ring gear andbe slideable on the main shaft to engage one of the first main shaftring gear and the second main shaft ring gear. The synchronizer locksthe first main shaft ring gear to the main shaft when the first drivechain is in the first drive chain engaged state, and locks the secondmain shaft ring gear to the main shaft when the second drive chain is inthe second drive chain engaged state.

The main shaft ring gears 44, 45, 46, 47 in this embodiment of the multiratio drive 100 rotate freely about the main shaft 40. A synchronizer102, 103 is adjacent to one or two of the main shaft ring gears 44, 45,46, 47 and is operable to slide along the longitudinal axis of the mainshaft 40. The synchronizer 102, 103 can be switched between neutral andlocked states by sliding the synchronizer 102, 103 along the main shaft40. In the neutral state, the synchronizer 102, 103 is free to rotateabout the main shaft 40. In the locked state, the synchronizer 102, 103is locked to and rotates with the main shaft 40. The synchronizer 102,103 in the locked state engages one of the main shaft ring gears 44, 45,46, 47, so the engaged main shaft ring gear is in a locked state androtates with both the synchronizer 102, 103 and the main shaft 40. Thesynchronizer 102, 103 and the main shaft ring gears 44, 45, 46, 47 havecomplementary mateable portions so that the synchronizer 102, 103 andthe engaged main shaft ring gear turn together when the synchronizer102, 103 is pushed toward the main shaft ring gear. Thus, power passesfrom the main shaft 40, through the synchronizer 102, 103, the mainshaft ring gear, and the differential shaft ring gear in the drive chainto the differential shaft 50.

FIG. 3B, in which like elements share like reference numbers with FIG.3A, is a detailed side view of a synchronizer for use in a multi ratiodrive in accordance with the present invention. The synchronizer 102 canhave an inner hub 101 positively splined to and turned by the main shaftand an outer sleeve 105 that can slide along the inner hub 101 relativeto the longitudinal axis of the main shaft. The outer sleeve 105 slideslongitudinally to engage the adjacent main shaft ring gear withcomplementary mateable portions, such as gears, dog teeth gears, or thelike. The synchronizer 103 can be similar to or the same as thesynchronizer 102.

Referring to FIG. 3A, when one synchronizer, such as synchronizer 102,is used with two main shaft ring gears 44, 45, the synchronizer 102 islocated between the two main shaft ring gears 44, 45 with the neutralstate centered between the two main shaft ring gears 44, 45. Thesynchronizer 102 can be moved one direction along the main shaft 40 toenter the locked state and engage one of the two main shaft ring gears44, 45 and the other direction along the main shaft 40 to enter thelocked state and engage the other of the two main shaft ring gears 44,45. The synchronizer 103 can be used in the same manner as thesynchronizer 102, only with the two main shaft ring gears 46, 47. Whenthe synchronizer is used with a single main shaft ring gear, thesynchronizer is located adjacent the main shaft ring gear with theneutral state away from the single main shaft ring gear. Thesynchronizer can be moved along the main shaft toward the single mainshaft ring gear to enter the locked state and engage the single mainshaft ring gear.

The synchronizer 102, 103 can be moved longitudinally with a shift fork106, 107 riding in a groove 104, 105 in the outer surface of thesynchronizer 102, 103. The shift fork 106, 107 can be moved relative tothe housing 60 by an actuator 108, 109 such as a solenoid, actuator,vacuum motor, hydraulic motor, or the like. In one embodiment, theactuator 108, 109 is responsive to an actuator command signal from avehicle computer. The shift fork 106, 107 can also be instrumented withposition sensors providing shift fork position and movement indicationto the vehicle computer. In another embodiment, the synchronizer 102,103 can be moved longitudinally with levers, cables, or the like, asused to change gears in vehicles with manual transmissions.

Those skilled in the art will appreciate that in another embodiment thesynchronizers and shift forks can be omitted and the main shaft ringgears moved with a hydraulic clutch pack, such as a hydraulic clutchpack employing hydraulic cylinders as used in automatic transmissions.In one embodiment, the same pump that provides pressure to the automatictransmission can drive the hydraulic clutch pack, and the vehiclecomputer can also control the hydraulic clutch pack. The hydraulicclutch pack can be operable to engage one of the first main shaft ringgear and the second main shaft ring gear, locking the first main shaftring gear to the main shaft when the first drive chain is in the firstdrive chain engaged state and locking the second main shaft ring gear tothe main shaft when the second drive chain is in the second drive chainengaged state.

FIGS. 4A and 4B, in which like elements share like reference numberswith FIG. 1, are cutaway side views of multi ratio drives in accordancewith the present invention. Referring to FIG. 4A, the main shaft 40 ismounted above the differential shaft 50 in the housing 60. Referring toFIG. 4B, the main shaft 40 is mounted behind the differential shaft 50in the housing 60. Those skilled in the art will appreciate that therelative positions of the main shaft 40 and the differential shaft 50can be selected as desired for a particular application.

FIG. 5, in which like elements share like reference numbers with FIG. 1,is a schematic diagram of another embodiment of a multi ratio drive inaccordance with the present invention. In this example, the multi ratiodrive 110 is the embodiment described for FIG. 1 above, with thecomponents scaled to approximate their actual relative dimensions. Themain shaft ring gears 44, 45, 46 can be switched between the engaged anddisengaged states using slip clutches, which are responsive torotational speed (rpm) of the main shaft 40 or centrifugal force toengage and disengage the main shaft ring gears 44, 45, 46 with the mainshaft 40. Each of the drive chains 73, 74, 75 can have different gearratios (from tooth spacing, diameter, and the like) to allow the multiratio drive 110 to operate at different gear ratios between the driveshaft 72 and axles 56, 57. Each of the drive chains 73, 74, 75 can alsohave different thicknesses to meet torque requirements. For drive chains73, 74, 75 with a higher gear ratio used to start vehicle motion and atlower vehicle speeds, the drive chain can be thicker to meet the hightorque demand. For drive chains 73, 74, 75, 76 with a lower gear ratioused when the vehicle is in motion, the drive chain can be thinner sincethe torque demand is less. The components of the multi ratio drive 110can be sized to fit within a conventional housing 60 currently in usefor vehicles, so the multi ratio drive 110 can be retrofit to vehiclescurrently in use.

FIG. 6 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention. In this embodiment, themulti ratio drive includes a housing; a piston longitudinally slideablein the housing; and a ring gear shell longitudinally slideable androtatably fixed in the housing. The ring gear shell is coupled to thepiston. The first drive chain includes a first sun gear, a first planetgear, and a first ring gear. The first sun gear is disposed on a sungear shaft. The first planet gear is engaged with the first sun gear, isrotatable about the sun gear shaft, and is operably connected to rotatea planet carrier about the sun gear shaft. The first ring gear isengagable with the first planet gear, and is disposed on the ring gearshell. The second drive chain includes a second sun gear, a secondplanet gear, and a second ring gear. The second sun gear is disposed onthe sun gear shaft. The second planet gear is engaged with the secondsun gear, is rotatable about the sun gear shaft, and is operablyconnected to rotate a planet carrier about the sun gear shaft. Thesecond ring gear is engagable with the second planet gear, and isdisposed on the ring gear shell. The piston positions the ring gearshell to engage the first planet gear with the first ring gear when thefirst drive chain is in the first drive chain engaged state; and thepiston positions the ring gear shell to engage the second planet gearwith the second ring gear when the second drive chain is in the seconddrive chain engaged state.

The multi ratio drive 200 includes a sun gear shaft 210 with sun gears212, 214; planet assembly 220 with planet carrier 222 and at least twoplanet gears 224, 226; ring gear shell 230 with at least two ring gears232, 234; housing 240; piston 250; and bearing 260. The multi ratiodrive 200 can also include a differential 270 and axles 272, 274. Thehousing 240 can contain lubricant (not shown) for the components of themulti ratio drive 200 within the housing 240, with seals (not shown)where any components pass through the housing 240.

The sun gear shaft 210 is operably connected to a transmission outputgear (not shown), which turns the sun gear shaft 210. In this example,the sun gear shaft 210 is the drive shaft. The planet gears 224, 226 ofthe planet assembly 220 rotate on the sun gears 212, 214 of the sun gearshaft 210. The sun gears 212, 214 can be integral to or fixedly attachedto the sun gear shaft 210. The planet gears 224, 226 run freely aboutthe sun gears 212, 214 and project through the planet carrier 222. Thesun gear 212, planet gear 224, and ring gear 232 form one drive chain231, and the sun gear 214, planet gear 226, and ring gear 234 formanother drive chain 233. The drive chains can have different gear ratios(from tooth spacing, diameter, and the like). Each of the drive chainshas an engaged state and a disengaged state. In the engaged state, theplanet gear and associated ring gear of the drive chain, such as planetgear 224 and ring gear 232 or planet gear 226 and ring gear 234, arealigned and mesh together. In the disengaged state, the planet gear andassociated ring gear of the drive chain are not aligned and do not mesh,so the planet gear runs freely about the sun gear without engaging theassociated ring gear.

Power is transferred from the sun gear shaft 210 to the planet carrier222 when one of the drive chains is engaged. The planet gear meshes withthe associated ring gear of the engaged drive chain, so the planet gearof the engaged drive chain walks around the ring gear of the ring gearshell 230, thus rotating the planet carrier 222. The ring gear shell 230includes lugs (not shown) on the outside diameter, which ride in grooves(not shown) in the housing 240. The lugs are parallel to thelongitudinal axis of the sun gear shaft 210, so the ring gear shell 230can be moved along the longitudinal axis, aligning one or the other ofthe planet gears 224, 226 with the associated ring gear 232, 234 in thedrive chain. The piston 250, which is circumferential to the inside ofthe housing 240 and adjacent to the ring gear shell 230, can move thering gear shell 230 axially. The piston 250 can be moved by an actuator(not shown), such as a solenoid, actuator, vacuum motor, hydraulicmotor, or the like, responsive to a piston control signal from thevehicle computer. The piston 250 can include a seal, such as an O-ringor the like, about the outer circumference to allow the piston 250 toslide against the housing 240.

In operation, the transmission output gear turns the sun gear shaft 210.In one configuration, the drive chain including the sun gear 214, planetgear 226, and ring gear 234 is engaged and the other drive chainincluding the sun gear 212, planet gear 224, and ring gear 232 isdisengaged. The sun gear 214 drives the planet gear 226, which walksaround the ring gear 234, so the planet gear 226 rotates the planetcarrier 222. The planet gear 224 rotates around the sun gear 212 butdoes not transfer any power. The planet carrier 222, supported by thebearing 260, rotates the axles 272, 274 through the differential 54,which allows differential slip between the two axles 272, 274.

The gear ratio of the multi ratio drive 200 can be changed bydisengaging the presently engaged drive chain and engaging the otherdrive chain. Power to the transmission output gear can be released torelease the sun gear 214 in the presently engaged drive chain. Thepiston 250 can then move the ring gear shell 230 so the planet gear 224is aligned with and meshes with the ring gear 232, so the drive chainincluding the sun gear 212, planet gear 224, and ring gear 232 isengaged. The drive chain including the sun gear 214, planet gear 226,and ring gear 234 is disengaged. The sun gear 212 drives the planet gear224, which walks around the ring gear 232, so the planet gear 224rotates the planet carrier 222. The planet gear 226 rotates around thesun gear 214 but does not transfer any power. The planet carrier 222,supported by the bearing 260, rotates the axles 272, 274 through thedifferential 270, which allows differential slip between the two axles272, 274. Those skilled in the art will appreciate that a number ofpossible gear ratios can be provided, limited only by the spaceavailable in the housing 240 for the sets of drive chains. In oneembodiment, the piston 250 is biased with springs to return to apredetermined position when the actuator is not applying pressure to thepiston 250. In one example, the piston 250 can position the ring gearshell 230 to allow both of the drive chains 231, 233 to be disengagedwhen the actuator is not applying pressure to the piston 250. In anotherexample, the piston 250 can position the ring gear shell 230 to allowone of the drive chains to be engaged and the other of the drive chainsto be disengaged when the actuator is not applying pressure to thepiston 250. Exemplary uses of the multi ratio drive are larger frontwheel drive vehicles and the like.

FIG. 7, in which like elements share like reference numbers with FIG. 6,is an end view of a ring gear shell for a multi ratio drive inaccordance with the present invention. The ring gear shell 230 includesthe ring gear 234 about the inside diameter. Lugs 235 about the outerdiameter are mateable with grooves in the housing to allow ring gearshell 230 to slide axially relative to the housing without rotatingabout the longitudinal axis of the sun gear shaft, and change the gearratio of the multi ratio drive.

FIG. 8, in which like elements share like reference numbers with FIG. 6,is a side view of a sun gear shaft for a multi ratio drive in accordancewith the present invention. The sun gear shaft 210 includes sun gears212, 214. The sun gears 212, 214 can have different gearingcharacteristics, such as teeth per inch, angle, or the like, as desiredfor a particular application.

FIG. 9 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention. In this embodiment, themulti ratio drive includes a housing; a first piston longitudinallyslideable in the housing; and a second piston longitudinally slideablein the housing. The first drive chain includes a first sun gear, a firstplanet gear, and a first ring gear. The first sun gear is disposed on asun gear shaft. The first planet gear is engaged with the first sungear, is rotatable about the sun gear shaft, and is operably connectedto rotate a planet carrier about the sun gear shaft. The first ring gearis engagable with the first planet gear, is longitudinally slideable androtatably fixed in the housing, and is coupled to the first piston. Thesecond drive chain comprises a second sun gear, a second planet gear,and a second ring gear. The second sun gear is disposed on a sun gearshaft. The second planet gear is engaged with the second sun gear, isrotatable about the sun gear shaft, and is operably connected to rotatea planet carrier about the sun gear shaft. The second ring gear isengagable with the second planet gear, is longitudinally slideable androtatably fixed in the housing, and is coupled to the second piston. Thefirst piston positions the first ring gear to engage the first planetgear when the first drive chain is in the first drive chain engagedstate, and the second piston positions the second ring gear to engagethe second planet gear when the second drive chain is in the seconddrive chain engaged state.

The multi ratio drive 300 includes a sun gear shaft 310 with sun gears312, 314, 316; planet assembly 320 with planet carrier 322 and planetgears 324, 326, 328; ring gears 332, 334, 336; housing 340; pistons 350,352, 354; and bearing 360. The multi ratio drive 300 can also include adifferential 370 and axles 372, 374. The housing 340 can containlubricant (not shown) for the components of the multi ratio drive 300within the housing 340, with seals (not shown) where any components passthrough the housing 340.

The sun gear shaft 310 is operably connected to a transmission outputgear (not shown), which turns the sun gear shaft 310. The planet gears324, 326, 328 of the planet assembly 320 rotate on the sun gears 312,314, 316 of the sun gear shaft 310. The sun gears 312, 314, 316 can beintegral to or fixedly attached to the sun gear shaft 310. The planetgears 324, 326, 328 run freely about the sun gears 312, 314, 316 andproject through the planet carrier 322. The sun gear 312, planet gear324, and ring gear 332 form one drive chain 331; the sun gear 314,planet gear 326, and ring gear 334 form another drive chain 333; and thesun gear 316, planet gear 328, and ring gear 336 form another drivechain 335. The drive chains can have different gear ratios (from toothspacing, diameter, and the like). Each of the drive chains has anengaged state and a disengaged state. In the engaged state, the planetgear and associated ring gear of the drive chain (such as planet gear324 and ring gear 332, or planet gear 326 and ring gear 334, or planetgear 328 and ring gear 336) are aligned and mesh together. In thedisengaged state, the planet gear and associated ring gear of the drivechain are not aligned and do not mesh, so the planet gear runs freelyabout the sun gear without engaging the associated ring gear.

Power is transferred from the sun gear shaft 310 to the planet carrier322 when one of the drive chains is engaged. The planet gear meshes withthe associated ring gear of the engaged drive chain, so the planet gearof the engaged drive chain walks around the ring gear, thus rotating theplanet carrier 322. The ring gears include lugs (not shown) on theoutside diameter, which ride in grooves (not shown) in the housing 340.The lugs are parallel to the longitudinal axis of the sun gear shaft310, so the ring gears can be moved along the longitudinal axis,aligning one or the other of the planet gears 324, 326, 328 with theassociated ring gear 332, 334, 336 in the drive chain 331, 333, 335. Thepistons 350, 352, 354, which are circumferential to the inside of thehousing 340 and adjacent to each of the ring gears 332, 334, 336, canmove the ring gears 332, 334, 336 axially. Each of the pistons 350, 352,354 can be moved individually by an associated actuator (not shown),such as a solenoid, actuator, vacuum motor, hydraulic motor, or thelike, responsive to a piston control signal from the vehicle computer.The pistons 350, 352, 354 can include a seal, such as an O-ring or thelike, about the outer circumference to allow the pistons 350, 352, 354to slide against the housing 340.

In operation, the transmission output gear turns the sun gear shaft 310.In one configuration, the drive chain 333 including the sun gear 314,planet gear 326, and ring gear 334 is engaged and the other drive chains331, 335 are disengaged. The sun gear 314 drives the planet gear 326,which walks around the ring gear 334, so the planet gear 326 rotates theplanet carrier 322. The planet gears 324, 328 rotate around the sungears 312, 316 but do not transfer any power. The planet carrier 322,supported by the bearing 360, rotates the axles 372, 374 through thedifferential 370, which allows differential slip between the two axles372, 374.

The gear ratio of the multi ratio drive 300 can be changed bydisengaging the presently engaged drive chain and engaging another drivechain. Power to the transmission output gear can be released to releasethe sun gear 314 in the presently engaged drive chain 333. The piston350 can then move the ring gear 332 so the planet gear 324 is alignedwith and meshes with the ring gear 332, so the drive chain 331 includingthe sun gear 312, planet gear 324, and ring gear 332 is engaged. Thepiston 352 moves the ring gear 334 so the drive chain 333 including thesun gear 314, planet gear 326, and ring gear 334 is disengaged. The sungear 312 drives the planet gear 324, which walks around the ring gear332, so the planet gear 324 rotates the planet carrier 322. The planetgears 326, 328 rotate around the sun gears 314, 316 but do not transferany power. The planet carrier 322, supported by the bearing 360, rotatesthe axles 372, 374 through the differential 370, which allowsdifferential slip between the two axles 372, 374. Those skilled in theart will appreciate that a number of possible gear ratios can beprovided, limited only by the space available in the housing 340 for thesets of drive chains. In one embodiment, the pistons 350, 352, 354 arebiased with springs to return to a predetermined position when theactuator is not applying pressure to the pistons 350, 352, 354. In oneexample, the pistons 350, 352, 354 can position the ring gears 332, 334,336 to allow the drive chains to be disengaged when the actuator is notapplying pressure to the pistons 350, 352, 354. In another example, thepistons 350, 352, 354 can position the ring gears 332, 334, 336 to allowone of the drive chains 331,333, 335 to be engaged and the other of thedrive chains 331,333, 335 to be disengaged when the actuator is notapplying pressure to the pistons 350, 352, 354.

FIG. 10, in which like elements share like reference numbers with FIG.9, is a side view of a sun gear shaft for a multi ratio drive inaccordance with the present invention. The sun gear shaft 310 includessun gears 312, 314, 316. The sun gears 312, 314, 316 can have differentgearing characteristics, such as teeth per inch, angle, or the like, asdesired for a particular application.

FIG. 11 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention. In this embodiment,idler pinion gears are engaged and disengaged from an idler shaft usinga synchronizer. The first drive chain includes a first idler pinion gearengaged with a first differential ring gear. The first idler pinion gearis locked on a drive shaft when the first drive chain is in the firstdrive chain engaged state and is rotatable on the drive shaft when thefirst drive chain is in the first drive chain disengaged state. Thefirst differential ring gear is fixed on a differential assembly. Thesecond drive chain includes a second idler pinion gear engaged with asecond differential ring gear. The second idler pinion gear is locked onthe drive shaft when the second drive chain is in the second drive chainengaged state and is rotatable on the drive shaft when the second drivechain is in the second drive chain disengaged state. The seconddifferential ring gear is fixed on the differential assembly. Thesynchronizer is disposed on the drive shaft between the first idlerpinion gear and the second idler pinion gear, and is slideable on thedrive shaft to engage one of the first idler pinion gear and the secondidler pinion gear. The synchronizer locks the first idler pinion gear tothe drive shaft when the first drive chain is in the first drive chainengaged state, and locks the second idler pinion gear to the drive shaftwhen the second drive chain is in the second drive chain engaged state.

The multi ratio drive 400 includes an idler shaft 440 and a differentialassembly 450, both of which are rotatably supported in a housing (notshown). A transmission output gear 470 receives rotational power from atransmission output shaft 472 and transfers the power to an idler gear442 fixed to the idler shaft 440, rotating the idler shaft 440 about itslongitudinal axis. The idler shaft 440 also has two or more idler piniongears 444, 445, each of which has an engaged state and a disengagedstate as determined by a synchronizer 402. In the engaged state, theidler pinion gear 444, 445 is locked to and rotates with the idler shaft440. In the disengaged state, the idler pinion gear 444, 445 is freefrom and rotates about the idler shaft 440.

The idler pinion gears 444, 445 mesh with differential ring gears 452,453, which are fixed to and rotate with the differential assembly 450.The differential ring gears 452, 453 and idler pinion gears 444, 445form drive chains 446, 447. The drive chains 446, 447 can have differentgear ratios (from tooth spacing, diameter, and the like) to allow themulti ratio drive 400 to operate at different gear ratios between thetransmission output shaft 472 and axles 456, 457. In one embodiment, thedifferential assembly 450 includes a differential 454 operably connectedto the axles 456, 457 to allow differential slip between the two axles456, 457.

The idler pinion gears 444, 445 in this embodiment rotate freely aboutthe idler shaft 440. The synchronizer 402 is adjacent to the main idlerpinion gears 444, 445 and is operable to slide along the longitudinalaxis of the idler shaft 440. The synchronizer 402 can be switchedbetween neutral and locked states by sliding the synchronizer 402 alongthe idler shaft 440. In the neutral state, the synchronizer 402 is freeto rotate about the idler shaft 440. In the locked state, thesynchronizer 402 is locked to and rotates with the idler shaft 440. Thesynchronizer 402 engages one of the idler pinion gears 444, 445 in thelocked state, so the engaged idler pinion gear is in an engaged stateand rotates with both the synchronizer 402 and the idler shaft 440. Thesynchronizer 402 and the idler pinion gears 444, 445 have complementarymateable portions so that the synchronizer 402 and the engaged idlerpinion gear turn together when the synchronizer 402 is pushed toward theidler pinion gear 444, 445. Thus, power passes from the idler shaft 440,through the synchronizer 402, the engaged idler pinion gear 444, 445,and one of the differential ring gears 452, 453 to the differentialassembly 450.

The synchronizer 402 can have an inner hub (not shown) positivelysplined to and turned by the idler shaft 440 and an outer sleeve (notshown) that can slide along the inner hub relative to the longitudinalaxis of the idler shaft 440. The outer sleeve slides longitudinally toengage the adjacent idler pinion gear 444, 445. When the synchronizer402 is used with two idler pinion gears 444, 445, the synchronizer 402is located between the two idler pinion gears 444, 445 with the neutralstate centered between the two idler pinion gears 444, 445. Thesynchronizer 402 can be moved one direction along the idler shaft 440 toenter the locked state and engage one of the two idler pinion gears 444,445 and the other direction along the idler shaft 440 to enter thelocked state and engage the other of the two idler pinion gears 444,445. When the synchronizer 402 is used with a single idler pinion gear,the synchronizer 402 is located adjacent the idler pinion gear with theneutral state away from the single idler pinion gear. The synchronizer402 can be moved along the idler shaft 440 toward the single idlerpinion gear to enter the locked state and engage the single idler piniongear.

The synchronizer 402 can be moved longitudinally with a shift fork (notshown) riding in a groove 404 in the outer surface of the synchronizer402. The shift fork can be moved relative to the housing by an actuator(not shown), such as a solenoid, actuator, vacuum motor, hydraulicmotor, or the like. In one embodiment, the actuator is responsive to anactuator command signal from a vehicle computer. The shift fork can alsobe instrumented with position sensors providing shift fork position andmovement indication to the vehicle computer. In another embodiment, thesynchronizer 402 can be moved longitudinally with levers, cables, or thelike, as used to change gears in vehicles with manual transmissions.

In operation, the transmission output shaft 472 rotates the transmissionoutput gear 470, causing the idler shaft 440 to rotate through thetransmission output gear 470. When the idler pinion gear 444 is in theengaged state, the engaged idler pinion gear 444 rotates with the idlershaft 440 and drives the differential ring gear 452 associated with theengaged idler pinion gear 444 in the drive chain 446. The differentialring gear 452 rotates the differential assembly 450, which rotates theaxles 456, 457 through the differential 454. The idler pinion gear 445in the disengaged state rotates about the idler shaft 440, driven by thedifferential ring gear 453 associated with the disengaged idler piniongear 445 in the drive chain 447, but transfers minimal power. The gearratio of the multi ratio drive 400 can be changed by disengaging thepresently engaged idler pinion gear 444 and engaging the presentlydisengaged idler pinion gear 445 by moving the synchronizer 402. Thoseskilled in the art will appreciate that a number of possible gear ratioscan be provided, limited only by the space available in the housing forthe sets of drive chains. Exemplary uses of the multi ratio drive aresmaller front wheel drive vehicles and the like.

Those skilled in the art will appreciate that in another embodiment thesynchronizers and shift forks can be omitted and the idler pinion gearsmoved with a hydraulic clutch pack, such as a hydraulic clutch packemploying hydraulic cylinders as used in automatic transmissions. In oneembodiment, the same pump that provides pressure to the automatictransmission can drive the hydraulic clutch pack, and the vehiclecomputer can also control the hydraulic clutch pack. The hydraulicclutch pack can be operable to engage one of the first idler pinion gearand the second idler pinion gear, locking the first idler pinion gear tothe drive shaft when the first drive chain is in the first drive chainengaged state and locking the second idler pinion gear to the driveshaft when the second drive chain is in the second drive chain engagedstate.

FIG. 12, in which like elements share like reference numbers with FIG.11, is a schematic diagram of another embodiment of a multi ratio drivein accordance with the present invention. In this embodiment of themulti ratio drive 500, the idler shaft is the transmission output shaft540, on which the idler pinion gears 444, 445 and synchronizer 402 aredisposed. One of the drive chains 446, 447 can be engaged by moving thesynchronizer 402 longitudinally into a locked state which engages one ofthe idler pinion gears 444, 445. In another embodiment, the idler piniongears can be moved with a hydraulic clutch pack rather than asynchronizer.

FIG. 13 is a schematic diagram of another embodiment of a multi ratiodrive in accordance with the present invention. In this embodiment, thefirst drive chain includes a first idler pinion gear, a first slidingpinion gear, and a first differential ring gear. The first idler piniongear is fixed to an idler shaft. The first sliding pinion gear isengagable with the first idler pinion gear, and is fixed to a slidingshaft. The first differential ring gear is engagable with the firstsliding pinion gear, and is fixed to a differential assembly. The seconddrive chain includes a second idler pinion gear, a second sliding piniongear, and a second differential ring gear. The second idler pinion gearis fixed to the idler shaft. The second sliding pinion gear is engagablewith the second idler pinion gear, and is fixed to the sliding shaft;and the second differential ring gear is engagable with the secondsliding pinion gear, and is fixed to the differential assembly. Thesliding shaft positions the first sliding pinion gear to engage thefirst idler pinion gear and the first differential ring gear when thefirst drive chain is in the first drive chain engaged state, andpositions the second sliding pinion gear to engage the second idlerpinion gear and the second differential ring gear when the second drivechain is in the second drive chain engaged state.

The multi ratio drive 600 includes an idler shaft 640, a sliding shaft620, and a differential assembly 650, all of which are rotatablysupported in a housing (not shown). A transmission output gear 670receives rotational power from a transmission output shaft 672 andtransfers the power to an fixed idler gear 642 fixed to the idler shaft640, rotating the idler shaft 640 about its longitudinal axis. The idlershaft 640 also has two or more idler pinion gears 644, 645 fixed to theidler shaft 640.

The sliding shaft 620 has two or more sliding pinion gears 622, 623fixed to the sliding shaft 620, which can be moved longitudinally alongits axis relative to the idler shaft 640 and the differential assembly650. The sliding shaft 620 can be moved relative to the housing by anactuator (not shown), such as a solenoid, actuator, vacuum motor,hydraulic motor, or the like. The idler pinion gears 644, 645 mesh withthe sliding pinion gears 622, 623, which mesh with the differential ringgears 652, 653. The idler pinion gears 644, 645, sliding pinion gears622, 623, and differential ring gears 652, 653 form drive chains 646,647. The drive chains 646, 647 can have different gear ratios (fromtooth spacing, diameter, and the like) to allow the multi ratio drive600 to operate at different gear ratios between the transmission outputshaft 672 and axles 656, 657. In one embodiment, the sliding shaft 620can have a neutral state in which neither of the drive chains 646, 647are engaged. In one embodiment, the differential assembly 650 includes adifferential 654 operably connected to the axles 656, 657 to allowdifferential slip between the two axles 656, 657.

In operation, the transmission output shaft 672 rotates the transmissionoutput gear 670, causing the fixed idler gear 642 to rotate the idlershaft 640. When the sliding pinion gear 622 is in the engaged state sothat the drive chain 646 is engaged, the engaged sliding pinion gear 622is rotated by the idler pinion gear 644 and drives the differential ringgear 652. The differential ring gear 652 rotates the differentialassembly 650, which rotates the axles 656, 657 through the differential654. The drive chain 647 is disengaged, so the idler pinion gear 645,sliding pinion gear 623, and differential ring gear 653 rotate withtheir respective shafts, but are not engaged to transfer power. The gearratio of the multi ratio drive 600 can be changed by disengaging thepresently engaged sliding pinion gear 622 to disengage the drive chain646 and engaging the presently disengaged sliding pinion gear 623 toengage the drive chain 647 by moving the sliding shaft 620. Thoseskilled in the art will appreciate that a number of possible gear ratioscan be provided, limited only by the space available in the housing forthe sets of drive chains.

While the embodiments of the invention disclosed herein are presentlyconsidered to be preferred, various changes and modifications can bemade without departing from the scope of the invention. Those skilled inthe art will appreciate that the multi ratio drives illustrated in FIGS.1-5 can be used with rear wheel drive vehicles or any other applicationin which the drive shaft is at a right angle to the axle. Those skilledin the art will further appreciate that the multi ratio drivesillustrated in FIGS. 6-13 can be used with front wheel drive vehicleshaving a transaxle or any other application in which the drive shaft isparallel to the axle. The multi ratio drive can be so dimensioned to fitwithin the housing of existing single ratio drives, so the multi ratiodrive can be retrofit into existing vehicles. The scope of the inventionis indicated in the appended claims, and all changes that come withinthe meaning and range of equivalents are intended to be embracedtherein.

The invention claimed is:
 1. A multi ratio drive operably connecting adrive shaft and an axle, the multi ratio drive comprising: a first drivechain having a first drive chain engaged state and a first drive chaindisengaged state; a second drive chain having a second drive chainengaged state and a second drive chain disengaged state; and a powertake-off (PTO) having a PTO coupling gear engaged with the second drivechain; wherein the first drive chain drives the axle with a first gearratio between the drive shaft and the axle when the first drive chain isin the first drive chain engaged state and the second drive chain is inthe second drive chain disengaged state; and the second drive chaindrives the axle with a second gear ratio between the drive shaft and theaxle when the second drive chain is in the second drive chain engagedstate and the first drive chain is in the first drive chain disengagedstate; the first gear ratio is different from the second gear ratio; thefirst drive chain further comprises a first idler pinion gear operablyconnectable with a first differential ring gear, the first idler piniongear being operably connectable to an idler shaft and the firstdifferential ring gear being fixed on a differential assembly; and thesecond drive chain further comprises a second idler pinion gear operablyconnectable with a second differential ring gear, the second idlerpinion gear being operably connectable to the idler shaft and the seconddifferential ring gear being fixed on the differential assembly.
 2. Themulti ratio drive of claim 1 further comprising a synchronizer, wherein:the first idler pinion gear engages with the first differential ringgear, the first idler pinion gear being locked on the idler shaft whenthe first drive chain is in the first drive chain engaged state andbeing rotatable on the idler shaft when the first drive chain is in thefirst drive chain disengaged state; the second idler pinion gear engageswith the second differential ring gear, the second idler pinion gearbeing locked on the idler shaft when the second drive chain is in thesecond drive chain engaged state and being rotatable on the idler shaftwhen the second drive chain is in the second drive chain disengagedstate; the synchronizer is disposed on the idler shaft between the firstidler pinion gear and the second idler pinion gear, the synchronizerbeing slideable on the idler shaft to engage one of the first idlerpinion gear and the second idler pinion gear; the synchronizer locks thefirst idler pinion gear to the idler shaft when the first drive chain isin the first drive chain engaged state; and the synchronizer locks thesecond idler pinion gear to the idler shaft when the second drive chainis in the second drive chain engaged state.
 3. The multi ratio drive ofclaim 1 further comprising a hydraulic clutch pack, wherein: the firstidler pinion gear engages with the first differential ring gear, thefirst idler pinion gear being locked on the idler shaft when the firstdrive chain is in the first drive chain engaged state and beingrotatable on the idler shaft when the first drive chain is in the firstdrive chain disengaged state; the second idler pinion gear engages withthe second differential ring gear, the second idler pinion gear beinglocked on the idler shaft when the second drive chain is in the seconddrive chain engaged state and being rotatable on the idler shaft whenthe second drive chain is in the second drive chain disengaged state;the hydraulic clutch pack is operable to engage one of the first idlerpinion gear and the second idler pinion gear; the hydraulic clutch packlocks the first idler pinion gear to the idler shaft when the firstdrive chain is in the first drive chain engaged state; and the hydraulicclutch pack locks the second idler pinion gear to the idler shaft whenthe second drive chain is in the second drive chain engaged state. 4.The multi ratio drive of claim 1, wherein: the first idler pinion gearand the second idler pinion gear are fixed to the idler shaft; the firstdrive chain further comprises a first sliding pinion gear fixed to asliding shaft, the first sliding pinion gear being engagable with thefirst idler pinion gear and the first differential ring gear; the seconddrive chain further comprises a second sliding pinion gear fixed to thesliding shaft, the second sliding pinion gear being engagable with thesecond idler pinion gear and the second differential ring gear; thesliding shaft positions the first sliding pinion gear to engage thefirst idler pinion gear and the first differential ring gear when thefirst drive chain is in the first drive chain engaged state; and thesliding shaft positions the second sliding pinion gear to engage thesecond idler pinion gear and the second differential ring gear when thesecond drive chain is in the second drive chain engaged state.
 5. Themulti ratio drive of claim 1 wherein the idler shaft is the drive shaft.6. The multi ratio drive of claim 1 further comprising: an idler gearfixed to the idler shaft; and a transmission output gear fixed to thedrive shaft, the idler gear being engaged with the transmission outputgear.
 7. The multi ratio drive of claim 1 wherein the drive shaftincorporates a transmission output gear, the multi ratio drive furthercomprising a fixed idler gear fixed to the idler shaft, and the fixedidler gear engages with the transmission output gear.
 8. The multi ratiodrive of claim 1 wherein the axle comprises a first axle and a secondaxle operably connected to the first drive chain and the second drivechain through a differential.
 9. A multi ratio drive operably connectinga drive shaft and an axle, the multi ratio drive comprising: a firstdrive chain having a first drive chain engaged state and a first drivechain disengaged state; a second drive chain having a second drive chainengaged state and a second drive chain disengaged state; and a powertake-off (PTO) having a PTO coupling gear engaged with the second drivechain; wherein the first drive chain drives the axle with a first gearratio between the drive shaft and the axle when the first drive chain isin the first drive chain engaged state and the second drive chain is inthe second drive chain disengaged state; and the second drive chaindrives the axle with a second gear ratio between the drive shaft and theaxle when the second drive chain is in the second drive chain engagedstate and the first drive chain is in the first drive chain disengagedstate; the first gear ratio is different from the second gear ratio; thefirst drive chain comprises a first idler pinion gear engaged with afirst differential ring gear, the first idler pinion gear being lockedon a drive shaft when the first drive chain is in the first drive chainengaged state and being rotatable on the drive shaft when the firstdrive chain is in the first drive chain disengaged state, and the firstdifferential ring gear is fixed on a differential assembly; the seconddrive chain comprises a second idler pinion gear engaged with a seconddifferential ring gear, the second idler pinion gear being locked on thedrive shaft when the second drive chain is in the second drive chainengaged state and being rotatable on the drive shaft when the seconddrive chain is in the second drive chain disengaged state, and thesecond differential ring gear is fixed on the differential assembly; themulti ratio drive further comprises an idler pinion gear mover selectedfrom the group consisting of a synchronizer and a hydraulic gear pack;the idler pinion gear mover being operable to engage one of the firstidler pinion gear and the second idler pinion gear; the idler piniongear mover locks the first idler pinion gear to the drive shaft when thefirst drive chain is in the first drive chain engaged state; and theidler pinion gear mover locks the second idler pinion gear to the driveshaft when the second drive chain is in the second drive chain engagedstate.
 10. A multi ratio drive operably connecting a drive shaft and anaxle, the multi ratio drive comprising: a first drive chain having afirst drive chain engaged state and a first drive chain disengagedstate; and a second drive chain having a second drive chain engagedstate and a second drive chain disengaged state; wherein the first drivechain drives the axle with a first gear ratio between the drive shaftand the axle when the first drive chain is in the first drive chainengaged state and the second drive chain is in the second drive chaindisengaged state; and the second drive chain drives the axle with asecond gear ratio between the drive shaft and the axle when the seconddrive chain is in the second drive chain engaged state and the firstdrive chain is in the first drive chain disengaged state; the first gearratio is different from the second gear ratio; the first drive chainfurther comprises a first idler pinion gear operably connectable with afirst differential ring gear through a first sliding pinion gear, thefirst idler pinion gear being fixed to an idler shaft, the first slidingpinion gear being fixed to a sliding shaft, and the first differentialring gear being fixed on a differential assembly; the second drive chainfurther comprises a second idler pinion gear operably connectable with asecond differential ring gear through a second sliding pinion gear, thesecond idler pinion gear being fixed to the idler shaft, the secondsliding pinion gear being fixed to the sliding shaft, and the seconddifferential ring gear being fixed on the differential assembly; thesliding shaft positions the first sliding pinion gear to engage thefirst idler pinion gear and the first differential ring gear when thefirst drive chain is in the first drive chain engaged state; and thesliding shaft positions the second sliding pinion gear to engage thesecond idler pinion gear and the second differential ring gear when thesecond drive chain is in the second drive chain engaged state.
 11. Themulti ratio drive of claim 10 wherein the idler shaft is the driveshaft.
 12. The multi ratio drive of claim 10 further comprising: anidler gear fixed to the idler shaft; and a transmission output gearfixed to the drive shaft, the idler gear being engaged with thetransmission output gear.
 13. The multi ratio drive of claim 10 whereinthe drive shaft incorporates a transmission output gear, the multi ratiodrive further comprising a fixed idler gear fixed to the idler shaft,and the fixed idler gear engages with the transmission output gear. 14.The multi ratio drive of claim 10 wherein the axle comprises a firstaxle and a second axle operably connected to the first drive chain andthe second drive chain through a differential.
 15. The multi ratio driveof claim 1 further comprising a power take-off (PTO) having a PTOcoupling gear engaged with the second drive chain.